This invention provides an improved and simplified process for the treatment of non-metallic minerals, particularly phosphate, contained in an ore in which the starting particle size of the ore for processing ranges from about minus 20 mesh to colloidal size. Flocculation and flotation are known methods for treating ores, but non of the prior methods have been successful in providing an economical and simplified method for treating ore containing a significant fraction comprising a fine particle size, e.g. less than about 10 microns.
In particular, phosphate ores contain substantial quantities of very fine particles which renders treatment and recovery of the desired phosphate difficult. In known treatment methods for phosphate ore, the ore is first sized and then separated into a sand fraction and a waste slime portion. The particle size of the sand fraction typically ranges from about minus 20 mesh to about plus 150 mesh. The fine particles, minus 150 mesh down to colloidal size, are the rejected waste slime portion. This waste slime portion, containing approximately 10 to 40% of the phosphate contained in the starting ore material, is discharged into environmentally undesirable tailings ponds. Known methods of treating the slimes have typically involved processing them after separation from the larger sands. U.S. Pat. No. 4,235,709 discloses a treatment by selective flocculation for the fine fraction of phosphate ores. This patent teaches conditioning the ore with sodium silicate prior to the addition of water and a subsequent flocculation agent consisting of a cellulose derivative. U.S. Pat. No. 2,660,303 teaches a process of adding a sodium hydroxide dispersant to the slime, followed by starch to selectively flocculate the phosphate and recover it for separation. U.S. Pat. No. 3,302,785 discloses a process for treating Tennessee phosphate slimes by negative ion froth flotation followed by desliming the tailings and combining the tailings with the froth concentrate to provide an electric furnace feed. The process is not applicable to Florida phosphate slimes due to the lack of plus 325 mesh phosphate agglomerates in the Florida slimes. A. F. Colombo in "Dispersion-Flocculation Characteristics of Florida Phosphate Slimes," a U.S. Bureau of Mines report, discloses treating an alkaline, aqueous slurry comprising phosphate waste slimes at pH 8.5 to 10 with a dispersant and subsequently with a high anionic functionality cornstarch as a flocculating agent to recover 60-70 percent of the phosphate product, upgraded 2 to 5 percent. None of the above references teaches the advantage of utilizing an ore having a non-uniform particle size as a feed material for selective flocculation utilizing a nonionic flocculation agent. In addition, none of the references teach the use of a hydrophobic selective flocculating agent.
It is therefore, the object of the present invention to improve non-metallic mineral recoveries over those obtainable by known conventional methods.
A further object of this invention is to provide an improved and simplified method for phosphate recovery from phosphate ores by utilizing both coarser sands and previously waste slimes and subjecting the starting phosphate feed material to a selective flocculation process utilizing a hydrophobic flocculating agent.
A still further object of this invention is to provide an improved and simplified process for phosphate recovery from phosphate waste slime tailings.
The process of the present invention provides an excellent overall phosphate recovery of an upgraded product from a non-uniform size ore containing fine and colloidal size particles, previously unattainable in, for example, the Florida phosphate processing industries. Utilizing the minus 150 mesh to colloidal size particles of the ore according to the methods of the present invention increases phosphate yield and reduces tailing disposal problems now encountered in the Florida phosphate industries. Moreover, ore slimes, the minus 150 mesh to colloidal size particles, now contained in tailings ponds can be added to the larger sized particles to reclaim the approximately 10 to 40% phosphorus contained in the slimes.